Re: prerequisite ignored when running 'make' (alone)

[Federico Bruni]

Il giorno mar 9 mag 2017 alle 14:29, Paul Smith <address@hidden> ha 
scritto:
> On Tue, 2017-05-09 at 14:06 +0200, Federico Bruni wrote:
> >  ### Makefile ###
> >  all: doc
> >
> >  dependencies = $(shell find docs -type f)
> >
> >  doc: $(dependencies)
> >          echo "Something has changed in the docs/ directory!"
> >
> >  ### end ###
> >
> >
> >  It looks up the files in the docs/ directory and executes the doc
> >  target if any file is changed.
>
> As written here, that's not what it does.
>
> >  If I run 'make doc', it behaves as expected.
> >  If I run 'make', the target is executed every time, even if no file
> >  changed in docs/.
>
> I can't explain the difference in behavior.  In fact, the behavior of
> "make" (target is executed every time) is what I expect to happen no
> matter how you invoke make.
>
> Why?  Because make decides whether or not to rebuild something by
> comparing _file timestamps_.
>
> In this makefile you'll compare the timestamps of all the files under
> the "docs" directory to... what?

Ok, that's the point, of course.
In my real project I was confused because I happened to name the 
default target like the directory built by another target (not run by 
'make') and by other stuff specific of my project that I won't explain 
here.